Microwave electron beam tubes

ABSTRACT

A microwave electron beam tube having a high-frequency interaction section insulated from the collector section of the tube by a gap across which the electron beam passes, the collector being surrounded by water contained in a boiler. The gap is shunted by a capacitor of solid material with its electrodes outside the evacuated envelope of the tube. The boiler is mechanically and electrically connected to a metal flange and a further flange is electrically and mechanically connected to the collector. Inserted between the two flanges is a dielectric spacer which offers a high impedance to what would otherwise be large high-frequency current flowing between the two flanges thus reducing radiation from the boiler to a negligible level.

United States Patent [54] MICROWAVE ELECTRON BEAM TUBES 4 Claims, 1 Drawing Fig.

[52] US. Cl 313/22, 313/36 [51] Int. Cl llOlj 1/02 [50] Field olSearch 313/22, 36

Primary Examiner-Roy Lake Assistant Examiner--Darwin R. Hostetter Attamey--Baldwin, Wight & Brown ABSTRACT: A microwave electron beam tube having a highfrequency interaction section insulated from the collector section of the tube by a gap across which the electron beam passes, the collector being surrounded by water contained in a boiler. The gap is shunted by a capacitor of solid material with its electrodes outside the evacuated envelope of the tube. The boiler is mechanically and electrically connected to a metal flange and a further flange is electrically and mechanically connected to the collector. Inserted between the two flanges is a dielectric spacer which offers a high impedance to what would otherwise be large high-frequency current flowing between the two flanges thus reducing radiation from the boiler to a negligible level.

MICROWAVE ELECTRON BEAM TIUEE This invention relates to microwave electron beam tubes of the kind in which the so-called body of the tube, i.e. the highfrequency interaction section thereof, is insulated from the collector section thereof by a gap across which the electron beam passes on its way to the collector. The passage of the electron beam across the gap between the interaction section and the collector section of the tube would, if nothing were done to prevent it, cause the radiation of such substantial amounts of high-frequency energy as to cause troublesome interference with nearby electronic or other high-frequency apparatus. lt is therefore common practice to try to prevent this by shunting the gap by a vacuum dielectric capacitor constituted by a pair of closely spaced electrodes inside the evacuated envelope of the tube. However, because of the very limited space available inside the said envelope the practically permissible areas for these electrodes and therefore the extent to which capacitance can be increased by increasing the electrode area are also severely limited. There is also a severe limit to the extent to which capacitance can be increased by reducing the interelectrode spacing in the capacitor which has to withstand high voltage. Permissible reduction of capacitor interelectrode spacing is all the more limited because the electrodes, being near the gap, are subjected to electron bombardment and become heated. lt is difficult to remove this heat which can, therefore cause electrode distortion and consequent risk of arcing-over or short circuiting when the tube is in use. If a short occurs between the interaction and collector sections of the tube it is quite likely to be severely damaged and made useless.

Our previous UK. Pat. No. 1,134,424 describes and claims an invention which is aimed at overcoming these defects and according to our said prior invention a microwave electron beam tube of the kind in which the high-frequency interaction section thereof is insulated from the collector section thereof by a gap has the gap thereof shunted by a radiation reducing capacitor with a dielectric of solid material the electrodes of said capacitor being outside the evacuated envelope of the tube and encircling the tube in the neighborhood of said gap. According to a feature of our said prior invention a microwave electron beam tube of the kind in which the high-frequency interaction section thereof is insulated from the collector section thereof by a gap situated between said sections, in a metallic tubular member through which the electron beam passes includes a metallic member encircling the tube in the neighborhood of said gap and electrically connected to said tubular member on one side of said gap, and a second metallic member also encircling the tube in the neighborhood of said gap but electrically connected to the tubular member on the other side of said gap, said metallic members being spaced apart by and sandwiching between them a member of solid dielectric material, and three members constituting a capacitor which has a dielectric of solid material and which is outside the evacuated envelope of the tube and is in shunt with said gap.

Our said prior invention is generally satisfactory and provides substantial improvement over practice known prior to said invention. However, when our said prior invention, as described in our said prior specification 1,134,424 is applied to certain microwave tubes having vapor cooled collectorsnotably to certain high-power klystrons and traveling wave tubes of the vapor-cooled collector type-the extent of radiation suppression is found to be surprisingly less than was expected and is desirable. Vapor cooling-almost always steam cooling-of the collectors of high-power klystrons and traveling wave tubes is, of course, customary. In a typical known construction for providing steam cooling the end of the collector nearer the gap is fitted with a flange which is mechanically and electrically united therewith and the said collector is contained within, and spaced from, a surrounding vessel, usually called the boiler. The boiler, which has inlet and outlet pipes, has at one end a flange which is mechanically and electrically united therewith and this flange is held flat against the flange on the collector so as to form a watertight joint therewith. In this way the collector is enclosed in a cooling jacket. in use water is fed through the inlet pipe into the internal boiler space round the collector, is boiled into steam by the heat thereof, and the steam is drawn off through the outlet pipe, condensed by an external condenser, and the resultant water fed back to the inlet pipe.

if the said prior invention of our UK. Pat. No. 1,134,424 is applied, embodied as described in that specification to a highpower klystron or similar microwave tube having a collector which is vapor cooled by means of a boiler arranged in the manner just described and fitted round the collector, it is found that, when the tube is in use, high-frequency radiation still takes place from the neighborhood of the collector section. The full amount of undesired high-frequency radiation taking place from the tube is still much less if it is a tube in accordance with our said prior invention, than would occur from a comparable tube to which our said prior invention had not been applied, but nevertheless enough radiation to be undesirable in practice still occurs. While the present invention is not dependent for its utility upon the correctness and suffrciency or otherwise of the theory now to be advanced, it is believed that the boiler behaves as one-half of a large diameter short length dipole antenna which, although far from being of optimum dimensions for a dipole at the working frequency of the tube, gives rise to high-frequency radiation additional to that which occurs through the gap between the collector and the high-frequency interaction sections of the tube and which is dealt with by our aforesaid prior invention.

According to the present invention a microwave electron beam tube of the kind in which the high-frequency interaction section of the tube is insulated from the collector section thereof by a gap across which the electron beam passes on its way to the collector said collector having means for effecting vapor cooling thereof and wherein said gap is shunted by a capacitor having a dielectric of solid material and with its electrodes outside the evacuated envelope of the tube and encircling it in the neighborhood of said gap comprises, for the purpose of effecting such vapor cooling, a so-called boiler which surrounds said collector and has, mechanically and electrically united therewith, a part which adjoins a member which is mechanically and electrically united with said collector said part being however separated from said member by an interposed spacer of dielectric material, said part, spacer and member forming a watertight joint situated at or near that end of the boiler near the gap between the high-frequency interaction section and the collector section of the tube.

Preferably said part is constituted by an outwardly extending flange on the boiler and said member is constituted by an outwardly extending flange on the collector, the two flanges being assembled face to face with a flat dielectric spacer between them.

Preferably said part and the said member are held together and electrically connected to one another by electrically conductive bolts or the like which pass through the space.

Preferably spring contact means are provided for maintaining electrical contact between the aforesaid part and one of the electrodes of the radiation-reducing capacitor.

The present invention is illustrated in the accompanying drawing which is a diagrammatic view showing a portion of a steam-cooled klystron in accordance with the said invention. The drawing shows the portion of the collector section and boiler adjacent the gap between the high-frequency interaction section and the collector section of the tube. The rest of the klystron may be as known per se and needs no description or illustration in this specification.

Referring to the drawing, 4i is the metallic (normally copper) tubing through which the electron beam passes, 5 is the gap between the high-frequency interaction and collector sections of the tube, ti is a ceramic cylinder forming part of the evacuated envelope of the tube and surrounding the gap, and 7 and h are two metallic annular members which are secured vacuumtight on the copper tubing on either side of the gap 5 therein and between which the ceramic cylinder 6 is fixed in a vacuumtight manner. The collector (most of which is shown in dotted line) is referenced 3. Fixed on the tubing 4 at a position between the annular member 8 and the adjacent end 2 of the high-frequency interaction section of the tube is a metal annular member 9.

Twelve is a metal member of 2 section and consisting of two annular portions 12A and 12C joined by a cylindrical portion 12B. The inner end of the portion 12C of the member 12, which in use is at earth potential, is fixed to the outer end of the member 9. The portion 12A of the member 12 forms one electrode of the capacitor provided by the invention in our previous U.K. Pat. No. 1,134,424 the other electrode of which is provided by part of an L-sectioned member 13 and the dielectric of which is constituted by an interposed dielectric member 14.

Mechanically with the collector 3 and fitted on the same near the end adjacent the gap is a metal flange 20. Surrounding the collector 3 (the water space is indicated by shading) is a boiler 21 on which is fitted, so as to be mechanically and electrically united therewith, a metal flange 22 of the same external diameter as the flange 20. The boiler 21, like the collector 3, is shown broken away but the broken-away end of the said boiler is, of course, closed. inlet and outlet pipes (not shown) are provided to admit water to the space between the collector and the boiler and to lead generated steam away from that space to a steam condenser (not shown). The two flanges and 22 are separated by an interposed spacer 23 of dielectric material and the boiler is supported by conductive bolts or'the like 24 which pass through the interposed spacer 23 and also provide DC connection between the flanges 20 and 22, These bolts are pulled tight to provide a watertight seal at the joints between 20, 23 and 22 and also ensure that, in use, the flanges 20 and 22 and therefore the collector and the boiler, will be at the same DC potential. Spring fingers 11 carried by the plate 13 provide and maintain electrical contact between this plate 13 and the flange 22.

The dielectric spacer 23, which can be quite thin, separates the boiler flange 22 from the collector flange 20 and it is believed that, by offering high impedance to what would otherwise be substantial high-frequency currents flowing from the collector flange 20 to the outer surface of the boiler, reduce dipole radiation from the latter to a negligible level. The bolts or the like 24 do not provide effective paths for high-frequency currents such as would cause material dipole radiation from the surface of the boiler.

I claim:

1. A microwave electron beam tube of the kind in which the high-frequency interaction section of the tube is insulated from the collector section thereof by a gap across which the electron beam passes on its way to the collector, said collector having means for effecting vapor cooling thereof and wherein 7 said gap is shunted by a capacitor having a dielectric of solid material and with its electrodes outside the evacuated envelope of the tube and encircling it in the neighborhood of said gap said tube comprising for the purpose of effecting such vapor cooling, a so-called boiler which surrounds said collector and has, mechanically and electrically united therewith, a part which adjoins a member which is mechanically and electrically united with said collector said part being however separated from said member by an interposed spacer of dielectric material, said part, spacer and member forming a watertight joint situated at or near that end of the boiler near the gap between the high-frequency interaction section and the collector section of the tube.

2. A tube as claimed in claim 1 wherein said part is constituted by an outwardly extending flange on the boiler and said member is constituted by an outwardly extending flange on the collector, the two flanges being assembled face to face with a flat dielectric spacer between them.

3. A tube as claimed in claim 1 wherein said part and the said member are held together and electrically connected to one another by electrically conductive bolts or the like which pass throu hthes acer.

4. A tu e as c armed in claim 1 wherein spring contact means are provided for maintaining electrical contact between the aforesaid part and one of the electrodes of the radiation-reducing capacitor. 

1. A microwave electron beam tube of the kind in which the highfrequency interaction section of the tube is insulated from the collector section thereof by a gap across which the electron beam passes on its way to the collector, said collector having means for effecting vapor cooling thereof and wherein said gap is shunted by a capacitor having a dielectric of solid material and with its electrodes outside the evacuated envelope of the tube and encircling it in the neighborhood of said gap said tube comprising for the purpose of effecting such vapor cooling, a socalled boiler which surrounds said collector and has, mechanically and electrically united therewith, a part which adjoins a member which is mechanically and electrically united with said collector said part being however separated from said member by an interposed spacer of dielectric material, said part, spacer and member forming a watertight joint situated at or near that end of the boiler near the gap between the high-frequency interaction section and the collector section of the tube.
 2. A tube as claimed in claim 1 wherein said part is constituted by an outwardly extending flange on the boiler and said member is constituted by an outwardly extending flange on the collector, the two flanges being assembled face to face with a flat dielectric spacer between them.
 3. A tube as claimed in claim 1 wherein said part and the said member are held together and electrically connected to one another by electrically conductive bolts or the like which pass through the spacer.
 4. A tube as claimed in claim 1 wherein spring contact means are provided for maintaining electrical contact between the aforesaid part and one of the electrodes of the radiation-reducing capacitor. 